1. Field of the Invention
The invention relates to a fire detection system and to an aircraft equipped with such a system.
2. Discussion of the Background
Fire detection systems, for example in aircraft, traditionally comprise a detection unit (or FDU from the English “Fire Detection Unit”) that receives information items from a set of detectors covering an area to be monitored and processes them for transmission to a display module, in the case of aircraft situated in the cockpit of the plane.
In general, a set of identical detectors is distributed over the area to be protected; each detector is therefore associated with a particular zone of the area and delivers a determined value of an electric quantity (for example, such as the resistance that the detector forms in the electric circuit connecting it to the detection unit), depending on the information item to be transmitted about the state of the detector: normal operation, detector failure or presence of a fire in the zone in question.
The different detectors are traditionally connected in parallel to the detection unit, thus making it possible in particular to limit the wiring necessary for installation of the function over the entire area to be protected.
However, the connecting in parallel of identical detectors makes it impossible to differentiate, in the detection unit, the detector transmitting a particular signal.
Nevertheless, it is of interest to determine which detector is the source of a particular information item, not only so that the detected fire can be located but also so that a faulty detector can be identified precisely and quickly during maintenance.
Furthermore, in systems that use two redundant channels to transmit the information item, precise determination of the zone in which a fire is detected makes it possible to limit alert situations in case both information channels are signaling a fire in the same zone (and not as soon as a fire is detected by each channel in some zone of the area).
In order to meet these expectations at least in part without however, necessitating expansion of the wiring necessary for installation of two detectors, the invention proposes a fire detection system that comprises a detection unit capable of measuring an electric quantity between a first and a second terminal, and a first detector connected to the first and second terminals and capable of forming a first value of the electric quantity in a determined state of the first detector, characterized by a second detector connected to the first and second terminals and capable of forming a second value of the electric quantity in the said determined state and a third value of the electric quantity in another state distinct from the said determined state, the first value and the third value being different from the second value.
Thus, even though the two detectors are connected in parallel, the different values of the electric quantity (first value and second value) make it possible to determine, in the detection unit, which detector is in the determined state (or in other words, for example, by which detector the fire has been detected) and thus to locate the corresponding zone precisely. Furthermore, the changeover between this same second value and the third value makes it possible to detect a change of state of the second detector.
The changes of value of the same quantity thus make it possible to transmit the state and the location of a given detector simultaneously to the detection unit, even though a parallel connection is being used.
The determined state corresponds, for example, to the detection of a fire by the detector in question.
Alternatively, the determined state may be normal operation of the detector, in which case it will be possible to locate the detection of a fire by virtue of the location of the normally operating detector and then by deduction.
The determined state also may correspond to a failure of the detector in question, in which case locating of the detector facilitates maintenance.
In the case in which the determined state corresponds to detection of a fire, it can be additionally provided that the first detector is capable of forming a fourth value of the electric quantity in normal operation and that the second detector is capable of forming the third value of the electric quantity in normal operation, the third value being different from the fourth value. It can then be provided that the first detector is capable of forming a fifth value of the electric quantity in case of failure and that the second detector is capable of forming the same fifth value of the electric quantity in case of failure.
When a single detector has failed, it will be possible to locate it precisely by virtue of the difference between the third and fourth values.